This invention relates to a tape cassette which is most suitable for use in a recording/reproducing apparatus such as a video tape recorder or other information processing apparatus, and more particularly, to a tape cassette which has a front cover rotatably attached in the front of a cassette casing to protect the surface of a magnetic tape and a rear cover pivotally supported by the front cover so as to be moved in cooperation therewith and serving to cover the back of the magnetic tape with the opening and closing operations of the front cover. In this tape cassette, vertically movable plugs are inserted in through holes formed in the cassette casing so that, when the positions of these plugs are changed arbitrarily, an information detecting sensor provided in the video tape recorder is made to detect the positions of the plugs thus changed, thereby making it possible to confirm various cassette information such as the prevention of miserasing.
In this kind of tape cassette, in order to protect a magnetic tape stretched on the front side of the cassette main body, the magnetic tape is held between the front cover and the rear cover provided rotatably and openably in the front of the cassette main body. (See Japanese Utility Model Unexamined publication No. 60-194787, for example.)
A conventional tape cassette of the above-described type will be described below with reference to the drawings. Heretofore, this type of tape cassette has been constructed as shown in FIGS. 1 to 8.
In FIGS. 1, 2, 3 and 4, a tape cassette comprises a front cover 7, an upper half 1 and a lower half 2, in which tape cassette a pair of tape reels 3 (S side) and 4 (T side) on which a magnetic tape 5 is wound are encased. The front cover 7 has a substantially U-shaped form in cross section, and a pair of first fulcrum pins 7b are formed integrally on the insides of right and left lugs 7a extending from opposite ends of the front cover 7 and facing in parallel with each other, the fulcrum pins 7b extending inwardly while being coaxial with each other.
As shown in FIG. 2, the front cover 7 has a pair of brackets 7h formed on the inside of the top and located at positions close to the center thereof. A pair of pin holes 7s are formed in the lower portions of the brackets so as to be substantially coaxial with each other. A pair of support pins 8a provided at right and left opposite ends of a rear cover 8 are to be inserted into the pair of pin holes 7s, respectively, so as to make the rear cover 8 rotatable about the support pins 8a.
As shown in FIGS. 2 and 5, the opposite fulcrum pins 7b of the front cover 7 formed as described above are respectively brought into engagement with a pair of pin engaging holes 2i, if which are formed in right and left opposite side walls 2f, 1e of a cassette casing 6. A pair of second pins 8b are formed at right and left opposite ends of the rear cover 8 so as to be integral therewith and substantially coaxial with each other and are brought into engagement with guide grooves 11 for free sliding movement in the vertical direction. It is therefore possible to close/open the front and rear covers substantially simultaneously with respect to the magnetic tape 5 stretched on the front side of the cassette casing 6 with the rotary motion of the front cover.
Further, as shown in FIGS. 2 and 5, the front cover 7 is rotatably attached to the cassette casing by bringing the opposite first fulcrum pins 7b thereof into engagement with the pair of pin engaging holes 2i, 1f formed in the right and left side walls 2f, 1e of the casing so that it can rotate in directions a and a' through about 90.degree. between two positions where the cover is opened and closed as shown in FIG. 3, thereby serving to open and close a front opening of the cassette casing. As shown in FIG. 4, there is provided a gap 16 between the inside of one of the end lugs 7a of the front cover 7 and the side wall 2f of the cassette casing which faces on the lug concerned, and the front cover 7 is urged to rotate in the direction of closing the cover by means of a torsion coiled spring 10 fitted on the first fulcrum pin 7b. The torsion coiled spring 10 is engaged at one end 10b thereof with a spring stopper 7e projecting from the inside of one end 7a of the front cover 7 at a position in front of the first fulcrum pin 7b and at the other end 10a thereof with another spring stopper 1d formed integrally with another side wall 1a of the cassette casing located rearwards of the first fulcrum pin 7b.
Referring to FIGS. 2 and 3, following the opening and closing operations of the front cover 7 (bracket portions 7h), the rear cover 8 moves rotatively about the support shafts 8a while other support shafts 8b of the rear cover 8 are fitted and inserted into the guide grooves 11 formed in the lower half 2, and therefore, it is possible to forcibly open and close the cover at the rear of the magnetic tape. Namely, the support shafts 8b serve as the control shafts when the rear cover 8 is opened and closed.
Further, since the rear cover 8 is required to move smoothly when opened and closed, it becomes necessary to provide a proper play (clearance; not shown) between the guide groove 11 of the lower half 2 and the opening and closing control shaft 8b. However, too much play will result in the deterioration of the sealing performance between the rear cover 8 and the front cover 7, thereby to exert bad influence on the information recorded and stored on the magnetic tape due to dust and the like from the outside. Particularly when the cassette is turned upside down, there is a tendency to cause a space between the front cover 7 and the rear cover 8 attributable to the individual weight of the rear cover 8 itself, the size of the space being equivalent to the play.
A biasing coiled spring 12 is supported on the rotation support shaft 8a of the rear cover 8 with one end thereof pressed against the bracket 7h of the front cover 7 and the other end thereof pressed against the vicinity of the rotation control shaft 8b, and a play suitable for smooth rotation is provided between the movement control shaft 8b and the guide groove 11 as described above, and, at the same time, the rear cover 8 is applied with the biasing force to close the cover at all times. With the above construction, even if the tape cassette is used harshly, the sealing performance between the front cover 7 and the rear cover 8 is improved so that the information recorded and stored on the magnetic tape can be protected.
In FIG. 5, in the space of a gap 47 defined by projection 2h at the rear of the first fulcrum pin 7b at one end (lug) 7a of the front cover 7, a locking member 9 is rotatably attached. The locking member 9 is formed integrally with a pivot shaft 9a (second fulcrum) at its top end, a locking pawl 9k at its lower front and a lock releasing protrusion 9h at its rear bottom end. The pivot shaft 9a is brought into engagement with pin engaging holes 2g formed in the cassette casing so that the locking member 9 is made rotatable back and forth. Further, the locking member 9 is urged to rotate forwardly at all times by means of a spring 13. As shown in FIG. 6, in a state where the front cover 7 is closed, the locking pawl 9k of the locking member 9 is brought into engagement with a protrusion 7d, which is formed integrally with the lug 7a of the front cover 7 so as to project inwardly at a lower end position P.sub.2 located in rear of the first fulcrum shaft 7b, from behind and below, thereby locking the front cover in the nearly closed condition.
In FIG. 5, each of the engaging holes with which the first fulcrum pins 7b of the front cover 7 are brought into engagement consists of the substantially semicircular holes 1f and 2i formed in the vertical combining portions of the right and left opposite side walls 1e and 2f of the upper and lower halves 1 and 2. The engaging holes 2g with which the pivot shaft 9a of the locking member 9 is brought into engagement are formed in the substantially U-shaped locking member receiving wall portion provided in rear of the front cover 7 and formed at the upper end of one or both of the side walls of the lower half 2 so as to have a top-opened U-shaped form. By fastening together the upper and lower halves 1 and 2 with screws or the like with both first fulcrum pins 7b of the front cover 7 kept in engagement with the holes consisting of the upper and lower semicircular holes and with the right and left opposite ends of the pivot shaft (second fulcrum) 9a of the locking member 9 kept in engagement with the pin engaging holes, the front cover 7 and the locking member 9 can be rotatably attached separately without any possibility of their coming off.
As the tape cassette having the above construction is loaded into the VTR (not shown), a lock releasing member 14 which can project from the VTR side is made to come in contact with the lock releasing protrusion 9h (9j) of the locking member 9 as shown in FIG. 6, so that the locking member 9 is moved back rotatively about the pivot shaft 9a and the locking pawl 9k is disengaged from the protrusion 7d of the front cover to release the locked condition. Then, a cover opening member (not shown) formed on the VTR side is inserted into a space 16 defined between the front cover 7 and the cassette casing side wall stepped surfaces 1e, 2f so as to push up an end face 7p of the front cover 7 against the biasing torsion coiled spring 10 and, at substantially the same time, the bracket 7h formed integrally with the front cover 7 is rotated about the first fulcrum pin 7b and, further, the pushing force is transmitted to the support pin 8a of the rear cover 8 which is supported by the bracket 7h at all times. In this case, contrary to the cover closing operation, the rotation control pin 8b of the rear cover 8 is moved toward the upper part of the cassette within the guide groove 11 of the lower half 2 against the biasing force of the torsion coiled spring 12, so that the rear cover 8 which has been served to protect the back of the magnetic tape is separated therefrom and the front cover 7 is separated from the surface of the magnetic tape. In this way, the covers are removed to open an opening L, thereby completing the loading of the magnetic tape in the VTR.
Next, description will be given of the construction for the judgement of various types of cassette information such as the prevention of miserasing in this kind of conventional tape cassette, that is, the construction in which the cassette is formed with through holes at plural points thereof and in which vertically movable plugs are disposed in these through holes so that positions of the plugs can be changed as desired, by referring to the drawings.
Referring to FIGS. 9 and 13, the cassette casing 6 consists of the upper and lower halves 1 and 2, and the reels 3 and 4 on which the magnetic tape 5 is wound are rotatably encased in the cassette casing 6. The front cover 7 is rotatably attached to the front end portion of the cassette casing 6, and the rear cover 8 capable of being opened and closed following the rotation of the front cover is further attached thereto. In addition, the cassette casing 6 is formed with three vertical through holes 20' (21', 20") at points located on right and left of the front part thereof and at a point located at the center of the rear part thereof. The through holes 20', 21', 20" formed on the back side of the cassette at the points located on right and left of the front part thereof serve as reference holes for positioning when the cassette casing is to be loaded in the recording/reproducing apparatus such as the video tape recorder. Within these through holes 20' (21'), plugs 28' are inserted respectively, and within through hole 20", plug 28" is inserted.
Referring next to FIGS. 10a and 10b, each plug 28' is formed at its upper end with a tool insert groove 28b' and at its lower end with a protrusion 28d' which projects in the horizontal direction, and two upper and lower stepped portions 24' and 25' are formed in the through hole at different angular positions. The plug is to be inserted in the through hole while being urged by a spring so as to bring the horizontal protrusion at the lower end of the plug into engagement with either of the two upper and lower stepped portions 24' and 25'. By so doing, the vertical position of the plug in the through hole can be changed.
Referring to FIGS. 13, 10A and 10B, cylindrical projecting portions 18', 18" and 19', 19" are formed in the upper and lower halves 1' and 2', respectively, so as to meet at surface 29' and form the through holes 20',20", the surfaces 24' and 25' for restricting the vertical movement of the plug 28' (slit-like upper and lower positioning portions, the veritcal and angular positions of which differ from each other in the through hole), and, further, the positioning and sensor insertion holes 21' when the cassette is to be loaded in the VTR.
The plug 28' is formed in the top end part thereof with a crown portion 28a' and the tool insert groove 28b' which can be handled from the outside by means of a screw-driver 42' or the like, and a coiled spring 40' serving to apply an elastic biasing force is disposed around the cylinder part located between the crown portion 28a' and the lower end protrusion 28d'.
The through hole 20' serves both as the insertion hole through which the crown portion 28a' of the plug is to be moved elastically and as the rotative operation range of the tip end of the screw-driver.
Referring to FIGS. 10A to 12B, when it is intended to move within the cassette casing 6 the plug 28' which has the elastic coiled spring 40' disposed between the crown portion 28a' and the lower end protrusion 28d', the tip end of the screw-driver 42' is brought into engagement with the groove 28b' formed in the crown portion 28a' of the plug 28' from the outside so as to press down the plug 28' until the lower end protrusion 28d' of the plug 28' is engaged with and inserted into the insertion groove formed in the upper half 1 and goes downwards in the vertical direction beyond the lower surface of the cassette casing 6 against the elastic coiled spring 40' as shown in FIG. 11. In this state, the plug 28' is rotated about the axis thereof in the direction of R' through 180.degree. so as to fix the position of the lower end protrusion 28d' at the point where either of the slit-like positioning portions 24' and 25' is formed in the cassette casing 6 due to the elastic restoring force of the coiled spring 40'. In this way, the vertical position of the plug 28' can be changed within the through hole 21'.
On the other hand, a position detective sensor pin 41' is formed upright on the VTR apparatus for free vertical movement for transferring a signal to the VTR apparatus according to the vertical position at which the position detective sensor 41' comes in contact with the lower end portrusion 28d' of the plug 28' and, further, with a lower end surface 28e', so as to prevent the re-recording of information or the miserasing of the information recorded already on the magnetic tape.
FIG. 11 shows the operation for moving the plug 28' from the upper position 25' to the lower position 24'. Namely, in the state where the tip end of the screw-driver 42' is brought into engagement with the groove 28b' formed in the crown portion 28a' so as to press down the plug 28' until the lower end protrusion 28d' of the plug 28' is engaged with and inserted into the insertion groove formed in the upper half 1 and goes downwards vertically beyond the lower surface of the cassette casing 6 against the elastic coiled spring 40', the plug 28' is rotated in the direction of R' through 180.degree..
Then, as the plug 28' is moved to the position where the plug lower end portrusion 28d' engages with another vertical groove, the elastic restoring force generated by the coiled spring 40' is transmitted to the plug 28' so that the lower end protrusion 28d' is received in the lower positioning portion 24' as shown in FIGS. 12A and 12B. On the other hand, the operation for moving the lower end protrusion 28d' from the lower positioning portion 24' to the upper positioning portion 25' is reverse to the operation described in connection with FIG. 11, that is, in the state where the lower end protrusion 28d' is pressed down until it goes beyond the lower surface of the cassettte casing 6 due to the operation performed from above, the plug 28' is rotated in the direction opposite to the direction of R' through 180.degree. so as to make the lower end protrusion 28d' engage with the other vertical groove likewise. As a result, the lower end protrusion is received in the upper positioning portion 25' due to the elastic restoring force generated by the coiled spring 40.
However, the conventional tape cassette of this kind has the following problem. Namely, as shown in FIGS. 4 and 6, in the conventional tape cassette, it becomes necessary to provide the space 16 and the front cover face 7p for enabling, when the tape cassette is loaded in the VTR, the cover opening member (not shown) formed on the VTR side to open the front cover of the tape cassette after releasing the locked condition by the contact of the locking releasing member 14 with the releasing protrusion 9h (9j) of the locking member as shown in FIG. 6, and hence, it is necessary to provide a gap S between the cassette casing 6 and the front cover 7.
In FIG. 14, the tape cassette (casing 6) which comprises the above-described front cover 7 and the rear cover 8 is provided with the lugs 7a, first stepped surfaces 1e, 2f which are formed in one or both of the side walls of the cassette casing 6 and which have the thickness equal to that of the lug 7a on which the pivot shaft is formed, and tapered second stepped surfaces 1g, 2j which are formed forwardly of the first stepped surfaces 1e, 2f in the cassette casing, so that there can be assured and provided between the front cover lug 7a and the second stepped surfaces 1g, 2f the space 16 through which the front cover opening member formed on the VTR side is made to pass as well as the gap S. On the other hand, the front cover 7 is formed at the lower end thereof with the stepped surface 7p with which the cover opening member is made to come in contact.
As the cassette casing 6 is loaded in the VTR apparatus, the lock releasing member 14 of the VTR is made to come in contact with the lock releasing projection 9h (9j) of the locking member 9 of the tape cassette as shown in FIG. 6, so as to release the lock for preventing the front cover 7 from being opened. Then, as soon as the cassette casing 6 is positioned in the standard position in the VTR in a short time, the front cover opening member (not shown) formed on the VTR side is inserted through the gap S so as to perform the cover opening operation against the biasing torsion provided by biasing torsion coiled spring 10.
In FIG. 14, the front cover opening member formed on the VTR is required to have a proper width from the viewpoint of the strength. Further, in consideration of the scatter in the positional accuracy of attaching, the proper width S of the space 16 becomes necessary. Increase of the width S contributes to the improvement of the chucking reliability of the VTR at the time of opening the cover, but too large a width S interferes with the loading area for tape travelling in the cassette. Accordingly, it is necessary that the width S take a proper value which can satisfy these two conditions.
If an impact load is applied to the corner of the front cover 7 of the above-described tape cassette in the direction of W (when the tape cassette is dropped, for example) as shown in FIG. 14, not only is the lug 7a on which the pivot shaft of the front cover is formed deformed (moved) elastically within the gap S, but also, the corner of the front cover lug 7a is cracked, or the lug 7a is broken at the corner, so that it becomes impossible to open and close the front cover, resulting in the fatal defect of the cassette that the recorded information is lost due to exposure of the surface of the magnetic tape 5 to dust from the outside, fingerprint, moisture, smoke or the like.
Further, if a load is applied to the corner of the front cover 7 in the direction of W so that the lug 7a on which the pivot shaft is formed is deformed elastically within the gap S, if the strength of the corner is high enough to prevent the cracking, the reaction force causes the pivot shaft 7b of the front cover to come off from the cassette casing 6 or to be broken to make it impossible to open and close the front cover itself while the magnetic tape surface is being exposed, resulting in the fatal defect noted above.
Further, if a load is applied to the corner of the front cover in the direction of W so that the lug 7a on which the pivot shaft of the front cover is formed is deformed elastically within the gap S and the front cover corner, the pivot shaft 7b and the engaging holes 1f, 2i of the cassette casing have the impact strength, since the rear cover 8 itself and the movement thereof are held and controlled by a pair of guide shafts 8b between a pair of guide grooves 11 provided in the cassette casing 6 as shown in FIGS. 9 and 14, the impact force is transmitted to the brackets 7h formed on the inside of the front cover 7 for pivotally supporting the rotary shafts 8a of the rear cover, with the result in that the brackets 7h are broken so as to cause the rear cover 8 to be disengaged from the tape cassette. If the rear cover 8 is disengaged from the tape cassette, since the tape 5 is damaged and the back of the magnetic tape is exposed, the information recorded and stored is lost as mentioned before, resulting in the fatal defact as well.
The above-described conventional tape cassette further has the following problem. Namely, as shown in FIGS. 15 and 16, from the viewpoint of the design of the conventional tape cassette, in order to detect the terminal end of the tape reel, holes 7c and 2c through which the photodetective optical path is made to pass and which are formed in the front cover 7 and the cassette casing 6, must be aligned with each other when the front cover is fully opened. The locking protrusion 7d' formed beforehand integrally on the inside of one or both of the lugs 7a at the opposite side ends of the front cover 7 can be released from the cover closing condition after the front cover 7 is permitted to rotate upwards of the cassette casing at the time when the locking member 9 is temporarily rotated backwards of the cassette casing by an external means such as the releasing member 14 of the VTR, for example, as shown in FIG. 6, that is, at the time of releasing the locked condition. In this case, since the locking member 9 is always urged rotatively toward the front of the cassette (or in the direction of locking the cover) about the pivot shaft 9a by means of the spring 10 (13) or the like, if there is exerted no external constraining force to the biasing force Pb, the locking member 9 is allowed to move easily within the movable range as shown in FIG. 15. In consideration of the cumulative moving backlash of the cassette in the VTR and, further, the cumulative attaching backlash of the lock releasing member 14 and the like, it is easily possible to cause the lock releasing member 14 to strike at the air. As shown in FIG. 15, since the optical path 2c along which a ray of light is made to pass when the cover is opened is covered with the locking pawl 9k of the locking member and the vicinity thereof, it is impossible to detect the terminal end of the tape so as to bring about the malfunction. Further, as shown in FIG. 16, in case that the front cover tends to rotate in the cover closing direction due to the biasing force Pf' with the locking member being rotated forwardly of the cassette due to the biasing force Pb' of the spring 10 or the like, the locking protrusion 7d' formed on the inside of the front cover 7a comes into contact with a surface 9e of the locking member so that the front cover and the locking member are restrained unreasonably so as to be brought to a standstill relative to each other. If they are kept in this state, not only can the tape cassette not be ejected out of the VTR, but also, the VTR or the cassette casing may by damaged if ejection by force is tried. In addition, if the locking member 9 is returned to its regular position unexpectedly, the front cover is rotated in the cover closing direction irrespective of the position of the magnetic tape drawn out, with the result in that the magnetic tape is damaged to cause the information recorded and stored thereon to be lost. This is a serious defect that can take place whether the cassette casing exists inside or outside of the VTR.
In the state shown in FIG. 16, if it is tried to push the front cover by force in the cover closing direction, the abutting force between the front cover and the locking member is increased to damage either member, thereby making it impossible to fulfill the prescribed function.
Moreover, the conventional tape cassette of this kind has the following problem. Namely, as shown in FIG. 17, it is necessary in the first place to insert (or temporarily fit) the plug 28' in the cassette upper half 1. In this case, since the vertical insertion groove with which an upper surface 28c' of the plug lower end protrusion 28d' is brought into engagement is not formed in the through hole 20' of the cylindrical projecting portion 18', the plug 28' itself is inclined in the direction X within the range of the plug receiving portion 20' and, further, pressed down against the biasing force Z' produced by the coiled spring 40' until the lower end protrusion 28d' goes beyond the plug lower positioning portion 24' of the upper half 1, that is, the position of greater displacement. For this reason, the operation is very complicated and requires sufficient experience in practice.
Then, the upper and lower halves are to be coupled together and fastened with screw or the like. By so doing, after the plug 28' is moved vertically and rotated about the axis thereof through about 180.degree., the vertical position of the plug 28' can be changed. However, since the positioning portions 24' and 25' with and by which the plug lower end protrusion 28' is brought into contact and positioned are provided in the upper and lower halves, respectively, with their heights and angular positions being different from each other, the structure of molds becomes complicated and, at the same time, it is difficult to mold these halves, with the result in that the cost is increased and, further, it becomes liable to cause the scattering because the upper and lower positions are constructed by the combination of the upper and lower halves.
In addition, in case of changing the plug itself between the upper and lower positions, since the stroke is so long that the plug lower end protrusion 28d' must be moved down to the lower surface of the cassette casing 6', the elastic reaction force of the spring becomes large naturally with the increase of the stroke, resulting in the operational difficulty as well.
Moreover, since the upper and lower halves are simply joined face to face with each other, if an unexpected high load is applied to the cassette casing 6 due to drop impact or the like, an offset U is caused due to disagreement between the cylindrical projecting portions of the upper and lower halves as shown in FIG. 18, so that the plug 28' assumes an aspect reverse to that assumed when it is temporarily fixed in the upper half. As a result, a spring biasing reaction force is exerted on the plug 28' so that the plug 28' is disengaged upwards from the cassette casing, thereby giving rise to a fatal defect that the prescribed function cannot be fulfilled.